Optical module, method of manufacturing the same, and sleeve

ABSTRACT

An optical module comprises a plastic package constituted by a package main body and a cover, sleeves formed integrally with the package main body, a circuit board held in the package main body, light-activated elements fixed at predetermined positions of the circuit board, three projections formed integrally with an inner surface of the package main body and brought into contact with a periphery of the circuit board to position the circuit board, springs formed integrally with an inner surface of the package to press the periphery of the circuit board against the projections. Since the sleeve and the package main body are integrally formed by plastic molding, the number of components is reduced, thereby simplifying the assembling steps.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical module used in an opticalcommunication system such as an optical data link or an optical localarea network (LAN), which uses light as an information transmissionmedium.

2. Related Background Art

As optical modules used in an optical communication system, there are atransmission module using a light-activated element such as an LED or asemiconductor laser as an electrooptic converting element(light-emitting element), and a reception module using a light-activatedelement such as a pin-photodiode as a photoelectric converting element(light-receiving element). Such an optical module generally has alight-activated element such as a light-emitting element or alight-receiving element, electronic components electrically connected tothe light-activated element and arranged on a circuit board, a lenssystem, and a sleeve in which the end portion of an optical fiber isinserted. For an optical fiber with a fiber core having a diameter ofseveral tens μm, the light-activated element, the lens system, and thesleeve must be assembled at high precision. For this reason, an opticalmodule as shown in FIG. 1 is conventionally used.

The optical module shown in FIG. 1 has a cylindrical holding body 1. Theholding body 1 is formed of a metal such as stainless steel. A lens (notshown) is arranged in the holding body 1 at one end. The other endportion of the holding body 1 serves as a sleeve for receiving a ferrule(not shown) at the end portion of an optical fiber. A light-activatedelement 2 is fixed to the holding body 1 with an adhesive or the like.The light-activated element 2 is arranged such that the optical axes ofthe element 2, the ferrule connected to the holding body 1 and the lensare matched with each other.

The holding body 1 having the light-activated element 2 fixed therein issupported, together with a circuit board 3, by a package main body 4consisting of a ceramic or metal. The terminals of the light-activatedelement 2 are connected by soldering (not shown) to electroniccomponents 5 such as bare chip ICs mounted on the circuit board 3.

The package main body 4 has inner lead pins 6 mounted inside the body 4,and outer lead pins 7 mounted outside the body 4 and electricallyconnected to the inner lead pins 6. The inner lead pins 6 areelectrically connected to terminals on the circuit board 3 by soldering.The wiring pattern and the electronic components 5 are sealed by a lid8. Finally, a cover 9 is fixed to the package main body 4, therebycompleting the optical module.

In the conventional optical module as described above, thelight-activated element 2 is held by the holding body 1 formed of ametal cylinder. The holding body 1 is an independent member whichseparates from the package main body 4 having the circuit board 3mounted thereon and the cover 9. For this reason, there are manycomponents of the module, resulting in higher productive cost and lowerproductive efficiency.

Although not illustrated, an optical module is known in which a leadframe is used in place of a package main body and a cover. A circuitboard and a light-activated element are mounted in the lead frame, andall these components are integrally molded with a plastic (JapaneseUtility Model Laid-Open No. 2-126107). In this case, however, thelight-activated element and the circuit board are independent members,as in the optical module shown in FIG. 1. Therefore, the same problem asin FIG. 1 is present.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoptical module which can be easily and precisely assembled without usinga cylindrical metal holding body.

In order to achieve the above object, according to the presentinvention, the constituent components of an optical module areintegrally formed of a plastic. In this case, it is important to checkwhether a light-activated element such as a light-emitting element or alight-receiving element, a lens, and a sleeve can be precisely arrangedby plastic molding.

The present inventor made an examination based on FIG. 2 and found thata precision required to couple light with a quartz optical fiber(graded-index type, core diameter: 62.5 μm) could be ±15 μm in a planeperpendicular to the optical axis and ±50 μm in a direction parallel tothe optical axis. It was confirmed that, with this precision, theoptical module could be realized with the dimensional precision of theplastic molding.

FIG. 2 is a graph showing a relationship between a deviation in opticalaxis and an optical power wherein the quartz optical fiber and thelight-activated element are separated from each other by a predeterminedinterval. This graph was obtained in the following manner. Two lenseswere arranged between an end of the optical fiber and thelight-activated element. The lens far from the end face of the opticalfiber was defined as the first lens, and the lens closer to the end faceof the optical fiber was defined as the second lens. The first lens wasfixed, and the second lens was stationary with respect to the opticalaxis. In this state, the second lens was moved in the planeperpendicular to the optical axis, and variations in optical power oflight coupled to the optical fiber were checked. Referring to FIG. 2, L1represents an interval between the first lens and the second lens, andL2 represents an interval between the second lens and the optical fiber.FIG. 2 shows variations in power of light in five arrangements obtainedupon changing the position of the second lens along the optical axis. Asdescribed above, the present inventor found, from graphs indicated bysymbols Δ and , that a dimensional precision of ±15 μm was allowed inthe plane perpendicular to the optical axis, and a dimensional precisionof ±50 μm was allowed in the direction parallel to the optical axis. Thepresent invention has been made on the basis of this examination.

According to the present invention, there is provided an optical modulecomprising a plastic package, constituted by a package main body and acover for closing an open portion of the package main body, forreceiving and holding a connector plug connected to an optical fiber, asleeve formed integrally with the package main body by plastic moldingto receive an end portion of the optical fiber when the connector plugis held in the package main body, a circuit board held in the openportion of the package main body, a light-activated element fixed at apredetermined position of the circuit board, three projections formedintegrally with an inner surface of the package main body and broughtinto contact with a periphery of the circuit board to position thecircuit board, spring means formed integrally with an inner surface ofthe package to press the periphery of the circuit board against theprojections, and a condenser lens coaxially arranged in the sleeve.

In the optical module having the above arrangement, since the sleeve andthe package main body are integrally formed by plastic molding, thenumber of components is reduced, thereby simplifying the assemblingsteps. The circuit board is always supported by the projections at thepredetermined reference points. Therefore, when the light-activatedelement is arranged at the predetermined position with respect to thereference points, the light-activated element, the sleeve, and the lensare coaxially arranged.

According to the present invention, there is also provided a method ofmanufacturing an optical module having the above arrangement, comprisingthe steps of preparing a board supporting table having three positioningpins standing on a surface in substantially the same layout as that ofthe three projections, resting the circuit board on the surface of theboard supporting table, pressing the circuit board such that theperiphery of the circuit board is brought into contact with all thepins, and using contact points of the pins as reference points to fixthe light-activated element at a predetermined position with respect tothe reference points.

When the light-activated element is to be arranged on the circuit board,the positions where the circuit board is brought into contact with theprojections in the package main body, i.e., the reference points can beeasily specified by using the board supporting table having thepositioning pins arranged in the same layout as that of the projections.As a result, the light-activated element can be arranged at a positionwhere the light-activated element is aligned with the sleeve and thelens.

The present invention will become more fully understood from thedetailed description given hereinbelow and the attached drawings whichare given by way of illustration only, and thus are not to be consideredas limiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the following detailed description, reference will bemade to the attached drawings in which:

FIG. 1 is an exploded perspective view showing a conventional opticalmodule;

FIG. 2 is a graph showing variations in optical power or coupling powercaused by a deviation in optical axis;

FIG. 3 is an exploded perspective view showing an optical moduleaccording to a preferred embodiment of the present invention;

FIG. 4 is a partially cutaway plan view showing the optical module shownin FIG. 3 in a disassembled state;

FIG. 5 is a front view showing the optical module taken along a lineV--V in FIG. 4;

FIG. 6 is a rear view showing the rear surface of a package main body ofthe optical module taken along a line VI--VI in FIG. 4;

FIG. 7 is a sectional view taken along a line VII--VII in FIG. 4;

FIG. 8 is an enlarged perspective view showing a sleeve;

FIG. 9 is a perspective view showing a method of arranging alight-activated element on a circuit board;

FIG. 10 is a perspective view showing an optical module according toanother embodiment of the present invention;

FIG. 11 is a perspective view showing the optical module in FIG. 10,when viewed from a lower surface side;

FIG. 12 is a perspective view showing a package main body and a circuitboard of the optical module in FIG. 10; and

FIG. 13 is a perspective view showing a method of assembling the opticalmodule in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, like references characters designate likeor corresponding parts throughout the several views. Also in thefollowing description, it is to be understood that such terms as"front", "rear", "left", "right", "upper", and the like, are words ofconvenience and are not to be construed as limiting terms.

FIGS. 3 to 7 are views showing an optical module according to anembodiment of the present invention. This optical module is of atransceiver type which integrates a transmission module and a receptionmodule. Referring to FIG. 3, reference numeral 10 designates an entirepackage formed by plastic molding. The package 10 comprises a packagemain body 12 and a cover 14 and serves as an optical connectorreceptacle for receiving connector plugs (not shown) provided at the endportions of transmission and reception optical fibers (not shown) to beconnected. A circuit board 20 having ICs (not shown), a light-emittingelement 16, a light-receiving element 18, and the like fixed thereon canbe mounted in the package 10.

The package main body 12 is of a rectangular prism shape orparallelepiped box shape and has a pair of side plates 22 and 23arranged parallel to each other, an upper plate 24 and a bottom plate26. The upper and bottom plates 24 and 26 are arranged between the upperedges and between the lower edges of the side plates 22 and 23,respectively, to be parallel to each other. As is apparent from FIG. 7,the side plates 22 and 23 and the upper plate 24 have almost the samelength. The bottom plate 26 is shorter than the side plates 22 and 23and the upper plate 24. One end of the bottom plate 26 is separated fromthe corresponding end portions of the side plates 22 and 23 and theupper plate 24 by a predetermined distance. A lateral plate 28 isarranged between the side plates 22 and 23 to perpendicularly extendfrom the end portion of the bottom plate 26 to the upper plate 24.Therefore, one end portion of the package main body 12 is closed by thelateral plate 28. The other end portion of the package main body 12 isopen. The connector plug of the optical fiber is inserted into the openend portion. The open end portion side is conveniently referred to as afront side hereinafter. The side plates 22 and 23, the upper plate 24,the bottom plate 26, and the lateral plate 28 are integrally formed ofan appropriate plastic material.

A pair of sleeves 30 and 31 are arranged in the package main body 12 toreceive the ferrules (not shown) at the end portions of the opticalfibers and align each ferrule with the light-emitting element 16 or thelight-receiving element 18 (to be described later). The sleeves 30 and31 are parallelly arranged in the lateral direction to be separated fromeach other by a predetermined interval and extend forward (the open endportion side of the package main body 12) from the front surface of thelateral plate 28. The sleeves 30 and 31 consist of the same plasticmaterial as that of the lateral plate 28 and the like and integrallyformed on the lateral plate 28. Through holes 32 and 33 are formed inthe lateral plate 28 at portions opposing the hollow portions of thesleeves 30 and 31. Together with the hollow portions of the sleeves 30and 31, the through holes 32 and 33 form continuous holes whichcommunicate the front inner portion to the rear inner portion of thepackage main body 12.

When the connector plugs of the optical fibers are inserted into thepackage main body 12 and held, the ferrules of the optical fibers areinserted into the corresponding sleeves 30 and 31 and supported by theinner surfaces of the sleeves 30 and 31 at desired positions. In thepresent invention, the sleeves 30 and 31 are not formed of a metal but aplastic, so the inner surfaces of the sleeves 30 and 31, which are incontact with the metal or ceramic ferrules, can be worn upon attachmentand detachment of the connector plugs. Particularly, the inner surfacesof the sleeves 30 and 31 must be precisely formed to determine theradial positions of the ferrules. For this reason, friction between thesleeves 30 and 31 and the ferrules is increased. In this embodiment, toprevent or reduce the friction on the inner surfaces of the sleeves 30and 31, a plurality of grooves 34 extending in the axial direction areformed in the inner surfaces of the sleeves 30 and 31, especially atportions in contact with the ferrule, and circumferentially spaced toeach other, as shown in FIG. 8. With this arrangement, the contact areawith respect to the ferrule is reduced, slidability is improved, and thewear of the contact surface is reduced. In addition, a tapered portion36 is preferably provided in the inner surface of the front end portionof the sleeve so that the ferrule can be smoothly inserted into thesleeve 30 or 31.

Lenses 38 and 39 are respectively arranged inside the sleeves 30 and 31,more particularly, at appropriate locations of the portions of thesleeves on which the ferrules do not abut. The lenses 38 and 39 arepositioned such that their optical axes match the longitudinal axes ofthe corresponding sleeves 30 and 31, respectively. The lens 38 mountedin the sleeve 30 opposing the light-emitting element 16 focuses lightfrom the light-emitting element 16 on the central portion of the endface of the corresponding ferrule, i.e., the end face of the fiber core.The lens 39 mounted in the sleeve 31 focuses light emerging from the endface of the reception optical fiber on the light-receiving surface ofthe light-receiving element 18.

The substantially rectangular circuit board 20 is arranged in a recessedportion (a portion defined by the inner surfaces of the side plates 22and 23, the inner surface of the upper plate 24, and the rear surface ofthe lateral plate 28) 40 on the rear end portion side of the packagemain body 12. The circuit board 20 in this embodiment consists of aceramic, an epoxy resin, or the like. A wiring pattern (not shown) isformed on the surface of the circuit board 20, and electronic components(not shown) such as ICs are mounted thereon. As shown in FIG. 3, acircuit on the circuit board 20 is electrically connected to an externalcircuit by a plurality of lead pins 42 extending from the lower edge ofthe circuit board 20.

In this embodiment, the light-emitting element 16 such as asemiconductor laser or a light-emitting diode and the light-receivingelement 18 are mounted on the surface of the circuit board 20 aslight-activated elements. The light-emitting element 16 and thelight-receiving element 18 are mounted such that the centers of thelight-emitting and light-receiving surfaces almost match the centralaxes of the corresponding sleeves 30 and 31 when the circuit board 20 isarranged at a predetermined position in the package main body 12. As iswell known, in order to improve optical coupling efficiency between thelight-emitting element 16 and the optical fiber, it is preferable toarrange a microball lens (not shown) at the center of the light-emittingsurface of the light-emitting element 16 and fix it with a transparentadhesive or the like. Alternatively, a light-emitting element having amonolithic lens may be used.

A transparent lid 44 of a plastic is fixed on the surface of the circuitboard 20 by an adhesive. The wiring pattern, the electronic components,and the light-activated elements 16 and 18 on the surface of the circuitboard are shielded from an atmosphere by the lid 44. The transparent lid44 has a rectangular flat plate portion 46 which is slightly smallerthan the circuit board 20, and a peripheral portion 48 formed integrallywith the peripheral edges of the flat plate portion 46 andperpendicularly depends therefrom. The end face of the peripheralportion 48 of the transparent lid 44 is bonded to the surface of thecircuit board 20. Therefore, a space is formed between the flat plateportion 46 of the transparent lid 44 and the surface of the circuitboard 20, and the light-activated elements 16 and 18 and the like arearranged in this space.

As described above, the circuit board 20 is arranged in the recessedportion 40 on the rear end portion side of the package main body 12. Thecircuit board 20 is accurately positioned by three positioningprojections 50 to 52 formed on the inner surface of the package mainbody 12. As is understood from FIG. 6, one of the projections 50 to 52is formed on the rear end portion side of the inner surface of the sideplate 23, and the remaining projections are arranged in the lateraldirection on the rear end portion side of the inner or lower surface ofthe upper plate 24 to be separated from each other by a predeterminedinterval. The projections 50 to 52 have a substantially semicircularsection and extend along the longitudinal direction of the package mainbody 12. The circuit board 20 is arranged in a state wherein itsperiphery is pressed against the projections 50 to 52 and positioned.More specifically, one long side of the rectangular circuit board 20,i.e., the upper edge is brought into contact with the projections 51 and52 on the upper plate 24 of the package main body 12. At the same time,one short side of the board 20, i.e., the right side edge in FIG. 3 isbrought into contact with the projection 50 on the side plate 23. Withthis arrangement, the circuit board 20 is supported at the three points,and its movements along two axial directions perpendicular to each otherand in the rotational direction are limited. Springs 54 to 56 forpressing the circuit board 20 against the projections 50 to 52 areintegrally formed on the rear end portion sides of the inner surfaces ofthe side plates 22 and 23 of the package main body 12. As shown in FIG.6, the spring 54 for pressing the circuit board 20 upward is formed, ata position adjacent to the lateral plate 28, on the inner surface of theside plate 23 having the projection 50. The spring 55 for pressing thecircuit board 20 upward and the spring 56 for pressing the circuit board20 toward the opposing side plate 23 are provided, at positions adjacentto the lateral plate 28, on the inner surface of the side plate 22.Various shapes of the springs 54 to 56 can be considered. In thisembodiment, each of the springs 54 to 56 is an arch-like projectingpiece having one end integrally fixed to the side plate 22 or 23. Whenthe circuit board 20 is arranged at a predetermined position to bringthe surface of the flat plate portion 46 of the transparent lid 44 intocontact with the rear surface of the lateral plate 28, the springs 54 to56 are brought into contact with the outer surface of the peripheralportion 48 of the transparent lid 44, thereby pressing the transparentlid 44. At this time, the springs 54 to 56 do not directly press thecircuit board 20. However, since the transparent lid 44 is fixed to thecircuit board 20, the pressing forces of the springs 54 to 56 act on thecircuit board 20 through the transparent lid 44, thereby pressing thecircuit board 20 against the projections 50 to 52. The circuit board 20pressed against the projections 50 to 52 by the springs 54 to 56 doesnot move in a plane defined by the surface of the circuit board 20.

The positions where the projections 50 to 52 are in contact with thecircuit board 20 are kept unchanged. For this reason, when thelight-emitting element 16 and the light-receiving element 18 arearranged at predetermined positions on the circuit board 20, thepredetermined position being previously determined on the basis of thecontact points as reference points, the light-emitting element 16 andthe light-receiving element 18 are always arranged on the central axesof the corresponding sleeves 30 and 31, respectively, at the time ofmounting the circuit board 20.

As described above, the package 10 of the optical module according tothe present invention has the cover 14. The cover 14 closes the rear endportion of the package main body 12 to hold the circuit board 20. Inthis embodiment, the cover 14 can be mounted at the rear end portion ofthe package main body 12 by dovetail joints. More specifically,dovetail-like projections 58 and 59 formed on the rear end surfaces ofthe side plates 22 and 23 of the package main body 12 are engaged withdovetail grooves 60 and 61 formed at the corresponding positions on thefront surface of the cover 14, thereby jointing the cover 14 and thepackage main body 12.

At least one (two in this embodiment) spring 62 is integrally formed onthe front surface of the cover 14. When the cover 14 is mounted on thepackage main body 12, the springs 62 press the lower surface of thecircuit board 20 forward. As a result, the circuit board 20 is pressedforward, and the front surface of the flat plate portion 46 of thetransparent lid 44 is brought into tight contact with the rear surfaceof the lateral plate 28, thereby arranging the circuit board 20 and thelateral plate 28 almost parallel to each other. With this arrangement,the circuit board 20 is prevented from being separated from the springs54 to 56 of the side plates 22 and 23, and at the same time, a deviationin optical axis is prevented. The lead pins 42 of the circuit board 20externally extend from a gap between the cover 14 and the bottom plate26 of the package main body 12 to enable connection to the externalcircuit.

As described above, when the optical module of this embodiment is used,the circuit board 20 is accurately positioned with respect to thepackage main body 12. For this reason, the light-emitting element 16 andthe light-receiving element 18 are coaxially arranged with thecorresponding sleeves 30 and 31 and the internal lenses 38 and 39,respectively.

As is apparent from the above description, when the circuit board 20having the light-emitting element 16, the light-receiving element 18,the electronic components, and the transparent lid 44 fixed thereon isarranged at a predetermined position in the package main body 12 andheld by the springs 54 to 56, and the cover 14 is mounted, the opticalmodule of the present invention can be easily manufactured. When thedimensional precision of an actually assembled optical module waschecked, it was confirmed that the dimensional precision among thesleeves, the lenses, and the light-activated elements was ±15 μm or lessin a plane perpendicular to the optical axis and ±50 μm or less in adirection parallel to the optical axis. This falls within a tolerance ofthe optical coupling efficiency when a quartz fiber (graded-index type,core diameter: 62.5 μm) is coupled to a light-activated element.

In case of the circuit board 20 of a ceramic, it is common that a largeceramic plate is divided along a predetermined line, thereby forming thecircuit board 20. Generally, the periphery of the circuit board 20obtained in this manner is not polished. Therefore, the size of thecircuit board 20 varies for each product, and each edge does not form aperfect line.

For this reason, it becomes difficult to accurately mount thelight-emitting element 16 and the light-receiving element 18 atpredetermined positions on the circuit board 20. If the light-emittingelement 16 and the light-receiving element 18 are inaccurately mountedon the circuit board 20, the light-emitting element 16 and thelight-receiving element 18 are not aligned with the correspondingsleeves 30 and 31 even if the circuit board 20 is arranged at apredetermined position in the package main body 12, as a matter ofcourse.

In the present invention, the light-emitting element 16 and thelight-receiving element 18 may be mounted on the circuit board 20 usingan apparatus as shown in FIG. 9. The light-activated element mountingapparatus in FIG. 9 includes a board supporting table 64 having a flatupper surface on which the circuit board 20 is to be mounted. Columnarpins 70 to 72 are mounted on and perpendicularly extend from the uppersurface of the board supporting table 64 in the substantially samelayout as that of the positioning projections 50 to 52 in the packagemain body 12. More specifically, the pins 70 to 72 are arranged suchthat points 50a, 51a, and 52a in FIG. 6 match points 70a, 71a, 72a inFIG. 9, respectively. These points is ones with which the circuit board20 is brought into contact. Therefore, when the circuit board 20 restson the board supporting table 64 such that a long side 20a and a shortside 20b of the circuit board 20 are brought into contact with the pins70 to 72, the contact points of the pins 70 to 72 match the contactpoints of the positioning projections 50 to 52, respectively. Using thecontact points as reference points, the light-emitting element 16 andthe light-receiving element 18 are arranged on the circuit board 20 atpositions determined in advance with respect to the reference points. Inthis case, upon mounting the circuit board 20 in the package main body12, the light-emitting element 16 and the light-receiving element 18 arearranged at predetermined positions in the package main body 12regardless of the shape of the circuit board 20.

When the light-emitting element 16 and the light-receiving element 18are to be actually mounted on the circuit board 20, first of all, thecircuit board is rested on the board supporting table 64. Thereafter,forces as indicated by arrows 74 to 76 are caused to act on the circuitboard 20, thereby holding the circuit board 20 on the board supportingtable 64. The light-emitting element 16 and the light-receiving element18 are fixed at predetermined positions using the contact points of thepins 70 to 72 as the reference points. When the light-emitting element16 and the light-receiving element 18 are to be fixed, a suitablemanipulator such as a robot arm having a collet at the distal endthereof is preferably used.

If the dimensional precision of the circuit board 20 is high, themounting positions of the light-emitting element 16 and thelight-receiving element 18 can be easily specified without using theabove-described light-activated element mounting apparatus. In thiscase, bottomed holes (not shown) can be formed at the element mountingpositions on the circuit board 20 in advance, and the light-activatedelements 16 and 18 can be fitted in the holes, thereby accuratelypositioning the light-activated elements 16 and 18. A ground electrodeor a lead electrode for inputting/outputting an electrical signal may beprovided by metallization or the like on the inner wall and the bottomsurface of the bottomed hole. Metallized portions may be formed to beused as the mounting positions of the light-activated elements 16 and 18without forming the bottomed holes.

The preferred embodiment of the present invention has been describedabove. The present invention is not limited to this embodiment, as amatter of course. The optical module of the above embodiment is a moduleused for both transmission and reception, and the light-emitting element16 and the light-receiving element 18 are arranged on one circuit board20. However, the present invention can also be applied to an opticalmodule having only one function of transmission or reception.

In the above embodiment, the springs 54 to 56 press the circuit board 20through the transparent lid 44. However, the springs may directly pressthe circuit board 20.

In the above embodiment, the springs 54 to 56 for pressing the circuitboard 20 against the positioning projections 50 to 52 are formed on thepackage main body 12. However, as in an optical module shown in FIGS. 10and 11, these springs may be arranged on the remaining membersconstituting the package. In the optical module in FIGS. 10 and 11, aspace portion 80 for arranging a circuit board 20' is formed at thecentral portion of a package main body 12' (FIG. 12). A cover 14' ismounted from the lower side of the circuit board 20' (FIG. 13). In thisarrangement, as shown in FIG. 13, a spring 56' for pressing the circuitboard 20' against a positioning projection 50' on a side plate 23' ofthe package main body 12' is provided on the inner surface of a sideplate 22', as in the above embodiment. However, springs 55' and 56' forpressing the circuit board 20' against positioning projections 51' and52' on the lower surface of the upper plate 24 are provided to the cover14'. In this case, when the cover is mounted, the circuit board 20' issimultaneously completely pressed against the projections 50' to 52', sothe optical module can be more easily manufactured.

As has been described above, according to the present invention, thesleeves and the package main body are integrally formed of a plastic,and the light-activated elements are fixed on the circuit board inadvance with this arrangement, the optical module can be assembled inthe number of manufacturing steps smaller than that of the prior art.Therefore, the optical module can be provided at lower cost. Inaddition, the package is formed of a plastic, so mass production can beachieved.

Furthermore, the circuit board is supported at the three points. Thisarrangement can cope with circuit boards having various shapes andsizes, so that a circuit board can always be supported at predeterminedreference points. Therefore, when the light-activated elements arearranged at predetermined positions corresponding to the referencepoints, the light-activated elements, the sleeves, and the lenses can becoaxially arranged.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

The basic Japanese Application No. 5-245479 filed on Sep. 30, 1993 ishereby incorporated by reference.

What is claimed is:
 1. An optical module comprising:a plastic packagefor receiving and holding a connector plug connected to an opticalfiber, said package including a package main body and a cover forclosing an open portion of said package main body; a sleeve formedintegrally with said package main body by plastic molding to receive anend portion of said optical fiber when said connector plug is held insaid package main body; a circuit board held in said open portion ofsaid package main body; a light-activated element fixed at apredetermined position of said circuit board; three projections formedintegrally with an inner surface of said package main body and broughtinto contact with a periphery of said circuit board to position saidcircuit board; spring means formed integrally with an inner surface ofsaid package to press said periphery of said circuit board against saidprojections; and a condenser lens coaxially arranged in said sleeve. 2.A module according to claim 1, wherein said circuit board issubstantially rectangular, one of said projections is in contact with afirst side of said circuit board, and remaining two of said projectionsare in contact with a second side of said circuit board, said secondside being adjacent to said first side.
 3. A module according to claim2, wherein said package main body is a box of a substantial rectangularprism shape, said one of said projections is formed on an inner surfaceof one side plate of said package main body, and said remaining two ofsaid projections are formed on an inner surface of an upper plate ofsaid package main body.
 4. A module according to claim 1, wherein saidspring means comprises a plurality of springs for pressing said circuitboard against said projections.
 5. A module according to claim 1,wherein, when said circuit board is substantially rectangular, one ofsaid projections is in contact with a first side of said circuit board,and remaining two of said projections are in contact with a second sideof said circuit board, said second side being adjacent to said firstside, said spring means comprises a spring formed integrally with aninner surface of the other side plate to press said circuit boardagainst said one of said projections, which is provided on said one sideplate, and a spring formed integrally with said inner surfaces of saidside plates to press said circuit board against said remaining two ofsaid projections, which are provided on said upper plate.
 6. A moduleaccording to claim 1, wherein said cover is mounted from a rear surfaceside of said circuit board arranged in said package main body.
 7. Amodule according to claim 1, wherein said cover is mounted from a lowerside of said circuit board arranged in said package main body.
 8. Amodule according to claim 7, wherein, when said circuit board issubstantially rectangular, one of said projections is in contact with afirst side of said circuit board, and remaining two of said projectionsare in contact with a second side of said circuit board, said secondside being adjacent to said first side, said spring means comprises by aspring formed integrally with an inner surface of the other side plateto press said circuit board against said one of said projections, whichis provided on said one side plate, and a spring formed integrally withsaid cover to press said circuit board against said remaining two ofsaid projections, which are provided on said upper plate.
 9. A moduleaccording to claim 1, wherein a transparent lid is fixed to said circuitboard to cover an electronic circuit and said light-activated element onsaid circuit board, and said spring means causes a pressing force to acton said circuit board through said transparent lid.
 10. A moduleaccording to claim 1, wherein said optical module is a transmissionmodule having a light-emitting element as said light-activated element.11. A module according to claim 1, wherein said optical module is areception module having a light-receiving element as saidlight-activated element.
 12. A module according to claim 1, wherein saidoptical module is a transmission/reception module having alight-emitting element and a light-receiving element as saidlight-activated element.
 13. A module according to claim 1, wherein aplurality of grooves are formed in an inner surface of said sleeve toextend in a longitudinal direction and circumferentially spaced to eachother.
 14. A method of manufacturing an optical module comprising aplastic package for receiving and holding a connector plug connected toan optical fiber, said package including a package main body and a coverfor closing an open portion of said package main body, a sleeve formedintegrally with said package main body to receive an end portion of saidoptical fiber when said connector plug is held in said package mainbody, a circuit board held in said open portion of said package mainbody, a light-activated element fixed at a predetermined position ofsaid circuit board, three projections formed integrally with an innersurface of said package main body and brought into contact with aperiphery of said circuit board to position said circuit board, andspring means formed integrally with an inner surface of said package topress said periphery of said circuit board against said projections,comprising the steps of:providing a board supporting table having threepositioning pins mounted on a surface in substantially the samearrangement as that of said three projections; resting said circuitboard on said surface of said board supporting table; pressing saidcircuit board such that said periphery of said circuit board is broughtinto contact with all said pins; defining contact points of said pins asreference points; and fixing said light-activated element at positionpredetermined with respect to said reference points.
 15. A methodaccording to claim 14, wherein said circuit board is substantiallyrectangular, one of said pins is in contact with a first side of saidcircuit board, and remaining two of said pins are in contact with asecond side of said circuit board, said second side being adjacent tosaid first side.
 16. A method according to claim 14, wherein saidlight-activated element is a light-emitting element.
 17. A methodaccording to claim 14, wherein said light-activated element is alight-receiving element.